My aunt, Kate Clunn, who has died aged 88, was a former mayor of Southwark and a redoubtable campaigner on local and national issues. Over the decades, she went through a significant political journey from being Southwark's answer to Barbara Castle, whom she resembled somewhat, to a prolific letter writer celebrated by Max Hastings in the Daily Mail as "the real Mrs Credit Crunch", for her advice on how to survive the economic slump.

She lived in south London for all but the last 18 months of her life – including 35 years on the notorious Aylesbury estate, Walworth – and was a fount of knowledge about the area and its working-class history.

Kate's family endured many tough years because of her father's unemployment during the Depression. The eldest of four surviving children, she passed the 11-plus but was unable to go to grammar school because her parents could not afford the extras the family was expected to pay for. Instead she left school at 14 and worked in Blackfriars, where she stuffed pools envelopes, and later in Fleet Street in the readers' letters department of the Daily Mirror.

Like my father, her brother Albert Murray, later an MP, she threw herself into local Labour politics. She became a Southwark councillor in 1945 and mayor in 1963. Her stint on the council came to an end after 37 years when, disillusioned with in-fighting in the Labour party, she joined the Social Democratic party and subsequently lost her seat.

She kept up her political interests, corresponding with everyone from the Archbishop of Canterbury to Norman Tebbit. Among her regular correspondents was the London mayor, Boris Johnson, and one of his recent letters to her begins: "Dear Kate, I'm afraid this is another occasion on which we will have to agree to disagree."

Kate's husband, Arthur, died in 1996. She is survived by her two sons, Roger and David, five grandchildren and a great-granddaughter.